Nothing is certain except death and taxes.

Except taxes aren’t certain. Not the amounts, not the timing, not the rules. And once you start pulling on that thread, the list of things we treat as certain, in our models and in our heads, gets uncomfortably long.

This is that list. It is not comprehensive, and it is not a claim that any of these things will change soon. The point is narrower and more useful: each item is something that felt impossible to imagine changing, right up until it changed. That feeling of impossibility is what this post is about, because the feeling is not evidence.

1. Taxes

South Africa introduced capital gains tax in 2001. Secondary tax on companies became dividends tax in 2012, at 15%, which became 20% in 2017. The corporate rate moved from 28% to 27% in 2023. VAT went from 14% to 15% in 2018, and in 2025 an announced further increase was scrapped after the political fallout, which is its own lesson: even the changes aren’t certain.

For life insurers the changes cut deeper. The four-fund tax basis arrived in 1993, and the risk policy fund was added from 2016, moving individual risk business from the I minus E basis to a corporate-style tax on profits. Anyone who had projected the tax cash flows of a risk book beyond 2016 on the old basis was simply wrong, through no fault of their modelling.

Yet most projection models take this year’s Income Tax Act and apply it to 2060. The amount of tax, the timing of tax, and the rules of tax all change, and they change more often than almost any other assumption we hold fixed.

2. Currency pegs

I worked in Lebanon in 2007. Insurers there held US dollar assets against Lebanese pound benefits, and pound assets against dollar benefits, and told me not to worry. There was no currency risk. The pound was pegged.

They had history on their side. The pound had been fixed at 1,507.5 to the dollar since 1997, a decade of perfect stability by the time I arrived, and it went on to hold for another twelve years. Then, from 2019, it lost more than 98% of its value, and the collapse took the banking system and those mismatched balance sheets with it. Dollar deposits became “lollars”, visible on the bank statement, inaccessible in practice.

Lebanon is not an isolated case. Sterling left the gold standard in 1931. The United States closed the gold window in 1971, ending Bretton Woods. Sterling was forced out of the ERM in 1992. Argentina’s one-to-one convertibility, in place for a decade and written into law, collapsed in 2002. And the Swiss franc’s floor against the euro, not even a peg, just a floor, was abandoned in January 2015 and the franc moved close to 20% in minutes, against the largest currency bloc in the world, in the middle of a trading day.

Against that record sits the Namibian dollar, pegged to the rand since 1993, along with the loti and lilangeni. Those pegs are fine. So far. Every peg on the broken list above was also fine, so far, right up until it wasn’t.

Judging pegs by the ones still standing is exactly the error. These are right truncated observations on data periods of hundreds of years. A peg that hasn’t broken is a censored data point, not a proof of safety. “Still pegged” only means the failure hasn’t been observed yet.

3. The biggest companies

None of the ten largest US companies of 50 years ago is in the top ten today. In 1975 the list was Exxon, General Motors, Ford, Texaco, Mobil, Chevron, Gulf Oil, General Electric, IBM and ITT. Oil and cars and machines, each one an institution nobody expected to be displaced.

Some fell further than merely out of the top ten. Kodak, a giant of that era, went bankrupt in 2012. Sears followed in 2018. General Electric, an original member of the Dow in 1896 and a continuous member from 1907, was removed from the index in 2018 after more than a century.

The investment crowd knows this statistic. It appears in every presentation on diversification and every argument for passive investing. But knowing it and believing it about today’s top ten are different exercises. Each of the 1975 giants looked as permanent then as the current ten look now, and the current ten look very permanent indeed.

4. Government debt

An A rating is meant to correspond to roughly a one in a thousand chance of default within three years. That figure comes from corporate rating transition studies, because the sovereign sample is too small to measure properly. Which is itself the point: there are so few rated sovereigns, and so few defaults among the well-rated ones, that a single Greece breaks the statistics.

And Greece happened. Rated A in 2009, restructured in 2012, with private creditors taking a haircut of more than half in the largest sovereign restructuring in history. Russia was investment grade weeks before its 2022 default. And for anyone who finds those examples comfortably foreign: South Africa defaulted in September 1985, freezing $13.6bn of foreign debt in the standstill that followed the Rubicon speech, with the financial rand resurrected to trap capital at home. The final payment on that 1985 debt was made in 2001, sixteen years later.

The usual response is that a government borrowing in its own currency cannot default, because it can print. Russia defaulted on its rouble-denominated GKOs in 1998. Printing was available. Default happened anyway, because default is a political decision as much as an arithmetic one.

We still discount liabilities on the government curve, hold government bonds at a zero capital charge for spread and default risk, and call the whole arrangement risk free. For most purposes that is a reasonable working convention. It is worth remembering that it is a convention.

5. Regulation

Not just the rules changing, which we half expect and occasionally even get consulted on. The interpretation and application of regulation can shift while the words stay identical.

Foreseeable dividends under SAM is a live example. The prudential standard has not changed. But the expected treatment has moved from deducting dividends from own funds once declared and near certain, to accruing an allowance for the coming year’s dividends through the quarterly QRTs. The SCR is unchanged, own funds are lower, and the reported cover ratio drops, on the same standard, for the same insurer, with the same balance sheet. Europe has seen the same dynamic: EIOPA has revised its guidance on matters like contract boundaries without any change to the underlying Directive.

This kind of shift is difficult to explain to a board. The regulation stayed the same but the answer moved. It sits in almost nobody’s risk register, precisely because the words on the page look so solid, and it arrives through industry letters, technical observations and supervisory feedback rather than through anything a legal review would catch.

6. Which power runs the world

Yes, this one is obvious. Persians, Greeks, Romans, Ottomans, British. Everyone knows empires end.

But obvious is not the same as internalised. A Roman in CE 50 could not have imagined Rome falling, and Rome had another four centuries in the west, and fourteen in Constantinople, of not falling to prove them right. In 1913 Britain ruled the largest empire the world had seen, close to a quarter of the map and of its people, and did not expect it to be dismantled within 50 years. India was gone by 1947 and most of the African colonies by the mid-1960s. The Soviet Union was a superpower until 1991, and then, within months, not a country.

Reserve currency status has already changed hands within the span of a long life: sterling held the position the dollar holds now, and lost it over the middle decades of the twentieth century.

Today, with the dollar in every reserve, US capital markets in every portfolio and Silicon Valley in every pocket, it is hard to feel that any of it could end. That difficulty is the whole point. It is exactly what certainty felt like in Rome, in London, in Moscow. I have no prediction to offer about when or how American primacy ends, and I would distrust anyone who does. The exercise is not prediction. The exercise is noticing that “I cannot imagine it” describes the limits of my imagination, not the limits of the world.

7. Whether to give your kids peanut butter

A palate cleanser, and a serious one. For years the official advice was to avoid peanuts in infancy, especially for high-risk children. The American Academy of Pediatrics recommended avoidance until age three in 2000. That guidance was withdrawn in 2008, and then the LEAP study in 2015 showed the opposite of the original advice: early exposure cut peanut allergy in high-risk infants by just over 80%, and by 2017 the formal guidance recommended deliberate early introduction.

Settled science on feeding children, followed conscientiously by a generation of parents, turned out to be not just wrong but inverted. If that can flip, the confident consensus in your own field deserves at least an occasional raised eyebrow.

The pattern

The pattern is not that things change. Everyone knows things change, and a list of changes is just trivia. The pattern is that each change was unimaginable the day before, to serious people with good information, and “unimaginable” turned out to be a statement about their imagination rather than about the world.

For those of us who build and rely on models, this has a practical edge. “Certain” in a model usually means “we chose not to model it”. Tax rules, the peg, the government curve, the supervisory interpretation: each is a variable somebody decided to hold constant. Sometimes that is a sensible choice. Modelling everything is neither possible nor useful, and a model that treats everything as uncertain tells you nothing.

But it is a choice, and it should be a conscious one. A worthwhile exercise, for an ORSA or simply for an afternoon: write down the certainties your model assumes, pick the one that feels most absurd to question, and ask what would happen if it moved. The one that feels most absurd is the interesting one. That feeling is the tell.

Even death only makes the certain list on outcome, not timing. Modelling the gap between the two is most of what actuaries do.

What belongs at number 8?